Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 170155 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 855 PM EST SUN NOV 16 2014 .SYNOPSIS...
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WEAK IMPULSES OF LOW PRESSURE WILL RIDE ALONG A STATIONARY FRONT POSITIONED SOUTHEAST OF THE CHESAPEAKE THROUGH THE OVERNIGHT HOURS. LOW PRESSURE OVER THE SOUTHEAST U.S. WILL TRACK NORTHEAST ACROSS THE REGION MONDAY...PULLING A COLD FRONT INTO THE WESTERN ATLANTIC BY EARLY MONDAY NIGHT. AN UPPER LEVEL TROUGH OF LOW PRESSURE WILL MOVE INTO THE REGION TUESDAY AND REMAIN THROUGH THE ENTIRE WEEK... WITH THE POTENTIAL FOR RECORD LOW MAXIMUM AND MINIMUM TEMPERATURES 10 TO 20 DEGREES BELOW NORMAL ON TUESDAY AND TUESDAY NIGHT.
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&& .NEAR TERM /THROUGH MONDAY/...
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THE INITIAL BLAST OF PCPN HAS PASSED THRU THE CWFA...AND PRESENTLY STRETCHES ACRS CENTRAL NJ WWD TO N-CENTRL MD. DUE TO THE LOW DEWPTS UPON PCPN ONSET...EVAP COOLING EFFECTS LED TO A MIX OF PTYPES. THAT HAS SINCE ENDED AS COLUMN HAS BECOME SATD. ALMOST ALL SITES OUTSIDE OF THE APLCNS ABV FRZG ATTM. WHILE THE BEST OF THE WAA WL CROSS THE MASON-DIXON LINE BY/SOON AFTR MIDNIGHT...ITS LEFT A VERTICAL TEMP PROFILE SUPPORTIVE OF JUST RAIN...AS EVIDENCED BY 00Z LWX RAOB. ADMITTEDLY THO...SITES BTWN 1000-2000 FT ON THE CUSP OF FZRA. PCPN WL BE MORE INTERMITTENT THRU THE OVNGT HRS. ISENT LIFT W/IN THTE RDG...ENHANCED BY WK S/WVS...WL BE THE PRIMARY FORCING MECHANISM. THE SFC CDFNT WL REMAIN W OF THE MTNS THRU THE NGT. AS SUCH...DONT THINK THERE WL BE MUCH TEMP CHG THRU THE NGT. THEREFORE...PTYPE FCST WL BE JUST RA THRU THE NGT. AFTER THE FIRST ROUND OF STEADY PCPN TONIGHT...ATTENTION THEN TURNS TO THE NEXT SLUG OF PCPN EXPECTED ON MONDAY AS THE SURFACE LOW PUSHES TO THE NORTHEAST AND A STRONG COLD FRONT SWINGS IN FROM THE WEST. THE 12Z MODEL RUNS KEEPING FAIRLY CONSISTENT WITH THE PAST FEW MODEL RUNS IN BRINGING IN THE HEAVIEST PCPN MONDAY MORNING...THEN TAPERING OFF IN THE AFTN AS THE FRONT PUSHES THROUGH...WITH ALMOST ALL PCPN OUT OF THE AREA BY 00Z TUES. A COUPLE THINGS OF NOTE FOR MONDAY. CONCERNING PCPN INTENSITY AND TYPE...THE SOUTHERLY FLOW TAPPING INTO A VERY MOIST AIRMASS WILL USHER IN VERY WARM AND MOIST...WITH PWATS APPROACHING 1.25 INCHES. SO PCPN TYPE WILL REMAIN RAIN DURING THE MORNING/AFTN HOURS WITH PERIODS OF MODERATE TO EVEN HEAVY RAIN ESP RIGHT ALONG WITH THE FRONT. WHILE NOT EXPECTING FLOODING ISSUES...COULD SEE NUISANCE FLOODING WITH THE MULTIPLE ROUNDS OF HEAVIER RAIN OVER LOWER LYING AREAS. AT THE VERY END OF THE PERIOD AS THE COLDER AIR RUSHES IN BEHIND THE FRONT...WILL START TO SEE A TRANSITION FROM RAIN TO SNOW SHOWERS MAINLY WEST OF THE ALLEGHENY FRONT. LLJ ALSO GREATLY INCREASES IN STRENGTH AHEAD OF THE FRONTAL SYSTEM...WITH BETWEEN 60-75 KT WINDS AT 850MB. WHILE A MORE STABLE AIRMASS WILL HELP KEEP MOST OF THIS ENERGY FROM REACHING THE SFC...A HEAVIER SHOWER COULD VERY WELL BRING DOWN SOME OF THE GUSTY-STRONGER WINDS. BOTH NAM AND GFS SOUNDINGS BETWEEN 18-21Z OVER FAR SOUTHEASTERN CORNERS OF THE CWA ALSO SHOW WEAK INSTABILITY...WHICH NOT ANTICIPATING THUNDER...BUT COULD SEE LOW TOP CONVECTION FORMING RIGHT ALONG THE FRONT.
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&& .SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/... THE NORTHERN AND SOUTHERN STREAMS WILL CONTINUE TO PHASE MONDAY EVENING AS A COLD FRONT EXITS EAST OF THE MID-ATLANTIC. RAIN WILL TAPER OFF ACROSS SOUTHERN MARYLAND AND SURROUNDING WATERS MONDAY EVENING. A STRONG PRESSURE GRADIENT WILL MOVE INTO THE REGION BEHIND THE COLD FRONT RESULTING IN GUSTY NW WINDS. GUSTS UP TO 45-50 MPH ARE POSSIBLE FOR ELEVATIONS ABOVE 2K FT. A WIND ADVISORY MAY BE POSSIBLE FOR RIDGE LINES MONDAY NIGHT INTO TUESDAY. GUSTS UP TO 35 MPH ARE POSSIBLE FURTHER EAST AND CLOSER TO SEA LEVEL. UPSLOPE SNOW SHOWERS WILL CONTINUE MONDAY EVENING AS THE UPPER LOW PASSES OVER THE GREAT LAKES. TEMPERATURES ARE EXPECTED TO PLUMMET TO THE TEENS ACROSS THE WESTERN SLOPES AND MEASURING SNOW WILL BE DIFFICULT. VISIBILITY WILL LIKELY DROP IN SNOW SHOWERS. THE UPPER LOW WILL MOVE ACROSS THE REGION. HIGH PRESSURE IS EXPECTED TO MOVE EASTWARD AND TO THE SOUTH BY TUESDAY EVENING. A PRESSURE GRADIENT WILL CONTINUE ACROSS THE REGION AND W WINDS WITH GUSTS UP TO 30 MPH ARE EXPECTED. UPSLOPE SNOW SHOWERS SHOULD TAPER OFF BY TUESDAY EVENING. TOTAL SNOW ACCUMULATIONS OF ONE TO TWO INCHES IS EXPECTED ALONG THE WESTERN SLOPES. COLD CONDITIONS ARE EXPECTED TUESDAY AND TUESDAY NIGHT. HIGH TEMPERATURES WILL RANGE FROM THE TEENS TUESDAY TO THE LOW TO MID 30S ACROSS I-95/SOUTHERN MD. HIGH PRESSURE WILL MOVE NORTHWARD TUESDAY NIGHT AND WINDS WILL DIMINISH SOME. TEMPERATURES IN THE TEENS ACROSS THE MTNS TO THE 20S ARE EXPECTED INTO WEDNESDAY MORNING. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... HIGH PRESSURE WILL MOVE OFFSHORE WEDNESDAY INTO WEDNESDAY NIGHT...WITH A VERY BRIEF AND SLIGHT MODERATION IN TEMPERATURES EXPECTED. MODELS ARE IN DISAGREEMENT AS TO HOW QUICKLY THE CORE OF THE COLDEST AIRMASS MODIFIES AND MOVES AWAY FROM THE AREA...WHICH LENDS A LITTLE UNCERTAINTY TO THE HIGH TEMPERATURE FORECAST WEDNESDAY...BUT REGARDLESS TEMPERATURES WILL STILL BE WELL BELOW NORMAL. A REINFORCING COLD FRONT MOVES THROUGH THURSDAY...BUT WITH VERY LITTLE MOISTURE TO WORK WITH PRECIPITATION CHANCES APPEAR LOW AT THIS POINT. A SECONDARY SHORTWAVE IN THE FAST AND PERTURBED FLOW WILL SWING ACROSS THE GREAT LAKES ON FRIDAY. THE ECMWF AND A FEW MEMBERS OF THE NAIFS HINT AT A WEAK WAVE OF LOW PRESSURE DEVELOPING OVER SOUTHERN VIRGINIA ON FRIDAY AND MOVING OFFSHORE. THIS SETUP WOULD LEND TO OVERRUNNING PRECIPITATION WHICH WOULD BE LIGHT GIVEN THE FAST FLOW AND LOW PRESSURE SCOOTING OUT TO SEA BEFORE IT CAN REALLY GET GOING. ANOTHER AREA OF HIGH PRESSURE AND SHOT OF COLD AIR WILL FOLLOW THIS SYSTEM FOR THE FIRST HALF OF NEXT WEEKEND...BEFORE THE HIGH SHIFTS OFFSHORE GIVING WAY TO POTENTIAL INCREASING STORMINESS BY THE END OF NEXT WEEKEND. && .AVIATION /02Z MONDAY THROUGH FRIDAY/...
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TERMINALS REMAIN IN VFR CONDS ATTM. HWVR...ONSET OF PCPN ERLR THIS EVNG HAS SATD AMS...AND XPCT LWRG FLGT CONDS-- BOTH CIGS AND VSBYS-- OVNGT. HV OPTED TO KEEP CONDS PRIMAILY NO LOWER THAN MVFR IN THE TAF THRU THE NGT. ACKNOWLEDGE THAT LIFR NOT TOO FAR OFF. IF FCST GOES STRAY...THAT WL PROBABLY BE HOW. MDT CONFIDENCE ON FORECAST DURING THE DAY MONDAY. HEAVIEST PCPN LOOKS TO MOVE THROUGH 13-19Z. FLGT CONDS WL DROP AOB IFR DURING THIS TIME. ONLY QSTN MARKS WL BE HOW LOW AND HOW PERSISTENT POOR CONDS WL BE. PCPN ENDING TIME SOMETIME BETWEEN 21-00Z AS THE COLD FRONT MOVES THROUGH...WITH CIGS/VIS IMPROVING QUICKLY IN THE WAKE OF THE PCPN/COLD FRONT. WINDS INCREASE FROM THE SOUTH DURING THE DAY...WITH PSBL GUSTS TO 20 KTS MIXING IN MIDDAY. THERE IS ALSO A CHC OF LLWS ISSUES MIDDAY AS LLJ CROSSES TERMINALS...SPCLY DC/BALT HUBS. HWVR...LLWS TOOL DID NOT INDICATE REQD CVRG...AND THUS DID NOT INCL IN TAFS. VFR CONDITIONS RETURN MONDAY NIGHT AND LAST THROUGH THURSDAY. GUSTY WINDS ON TUESDAY EVERYWHERE...WITH WEST WINDS GUSTING TO 25-35 KTS. WINDS LIGHTEN AND BECOME SOUTHERLY BY WED AS HIGH PRESSURE BUILDS INTO THE REGION. SUB-VFR CONDITIONS ARE POSSIBLE FRIDAY IF WEAK LOW PRESSURE MATERIALIZES TO THE SOUTH AS DEPICTED BY SOME GUIDANCE...WHICH WOULD SPREAD LOW CLOUDS AND PRECIPITATION OVER THE AREA.
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&& .MARINE...
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SLY FLOW GNLY AOB 10 KT ATTM. SUB-SCA CONDITIONS WILL CONTINUE THROUGH TONIGHT AHEAD OF APPROACHING MULTIPLE WEAK LOW PRESSURE SYSTEMS. HWVR...THE GRADIENT FLOW WL BE INCREASING THRU THE NGT AND INTO MON. SCA REMAINS IN EFFECT BGNG MON. HWVR...THE TREND OF INCRSG WND IN ADVC OF CDFNT SUGGESTS THAT THE STRONGER WND GUSTS WL COME DURING THE AFTN. A STRONG LLJ...WITH WINDS TO 70 KTS...SETS UP OVER THE WATERS MON AFTN...BUT WITH SUCH A STABLE AIRMASS IN PLACE...STILL UNSURE HOW MUCH OF THE ENERGY WILL REACH THE SFC. LTST MDL SNDGS SUGGEST NOT MUCH MORE THAN 30 KT. THUS...HV NOT UPGRADED TO GLW YET. A COLD FRONT WILL CROSS THE WATERS BY MONDAY NIGHT AND NW WINDS WITH BECOME GUSTY. GUSTS UP TO 35 KTS ARE POSSIBLE ESPECIALLY ACROSS THE MD CHESAPEAKE BAY. A SCA ADVISORY IS IN EFFECT THROUGH TUESDAY BUT GALE WARNINGS ARE POSSIBLE TUESDAY AFTERNOON. GUSTY CONDITION WILL LIKELY PERSIST TUESDAY NIGHT RESULTING IN SCA CONDITIONS. GUIDANCE INDICATES WINDS MAY ABATE SOMEWHAT WEDNESDAY MORNING...BEFORE WIND GUSTS TO SMALL CRAFT ADVISORY LEVELS PICK UP AGAIN LATER IN THE DAY AND INTO THE EVENING...LASTING THROUGH THURSDAY. WINDS THEN BECOME LIGHTER THURSDAY NIGHT INTO FRIDAY AS THE PRESSURE GRADIENT RELAXES AND A POTENTIAL WEAK WAVE OF LOW PRESSURE DEVELOPS TO THE SOUTH.
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&& .CLIMATE... A WAVE OF COLD AIR WILL MOVE ACROSS MUCH OF THE EASTERN PART OF THE CONUS DURING THE MIDDLE PART OF THE UPCOMING WEEK...AFFECTING OUR AREA WITH TEMPERATURES BETWEEN 10 AND 20 DEGREES BELOW NORMAL TUESDAY THROUGH WEDNESDAY. BELOW IS A LIST OF RECORD DAILY MINIMUM AND RECORD DAILY LOW MAXIMUM TEMPERATURES FOR THE DATES OF NOVEMBER 18TH (TUESDAY) AND 19TH (WEDNESDAY). SITE 11/18 MIN 11/18 LOW MAX 11/19 MIN 11/19 LOW MAX DCA 21 (1959) 30 (1924) 18 (1891) 33 (1880) BWI 20 (1959) 31 (1959) 20 (1936) 35 (1880) IAD 20 (1991) 39 (2008) 20 (1990) 38 (2008) && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 6 AM MONDAY TO 6 PM EST TUESDAY FOR ANZ530>543. && $$ SYNOPSIS...HTS/HAS NEAR TERM...HTS/SEARS SHORT TERM...HAS LONG TERM...DFH AVIATION...HTS/SEARS/HAS/DFH MARINE...HTS/SEARS/HAS/DFH CLIMATE...DFH

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